The purpose of this project is to undertake a systematic study of the interaction of follicle stimulating hormone (FSH) with specific receptors in rat testis. Highly purified human FSH (hFSH) or rat FSH (rFSH), iodinated under conditions which permit retention of biologic activity, will be utilized as the radioligand in these studies. The properties of the FSH receptor interaction will be investigated by techniques previously applied successfully to studies on LH-rat testes receptor interactions. Although initial experiments will be concerned with fundamental properties of specific FSH receptors in homogenate of rat testes tubules, the ultimate goal is to understand the nature of the FSH interaction with receptors in isolated seminiferous tubule membrane preparations and with receptors after solubilization and purification. Solubilization will be attempted through use of ionic and non-ionic detergents or various organic solvents. Chemical purification of the receptor will be pursued through use of a variety of methods, but it is hoped that affinity chromatography will allow a rapid advance in this area. The effect of variables such as pH, ionic strength and temperature on the kinetics and other aspects of hormone-receptor interactions will be examined and then a comparison will be made of properties of receptors in isolated membranes with those obtained after solubilization and purification. The chemical properties of the receptors will be probed through use of chemical and enzymatic modifications. The relationship of hormone binding and activation of the adenyl cyclase system will also be studied. Based on experiments with the rat system, initial attempts will be made to perform similar studies on FSH receptors in human and monkey testicular tissues. BIBLIOGRAPHIC REFERENCES: Leach, S.J., E. Minosian, L.E. Reichert, Jr. "Bovine luteinizing hormone: Circular dichroism studies and thermol difference spectra." Biochim. Biophysica Acta, 386:144-154 (1975). Reichert, L.E., Jr., and R.B. Ramsey. "Dissociation of human follicle stimulating hormone: Comparison with luteinizing hormone." J. Biol. Chem., 250:3034-3040 (1975).